The objective of this proposal is to study the role of Erbin in regulation of nicotinic acetylcholine receptor (AChR) synthesis and underlying mechanisms. Neuregulin (NRG) is a polypeptide essential for the maintenance of high concentration of the AChR at the neuromuscular junction (NMJ). It initiates signal cascades by stimulating ErbB protein tyrosine kinases in skeletal muscle cells and thereby activates Erk to induce the transcription ofAChR subunit genes. An important question yet to be addressed is how NRG signaling is regulated so that AChR is maintained at optimal level. We have recently identified Erbin, an ErbB2 interacting protein, which appears to inhibit Erk activation. Based on preliminary results, we hypothesize that Erbin may negatively regulate or switch off NRG-mediated expression of AChR subunit genes. Such regulatory mechanism may be important for preventing AChR from being over-expressed. This proposal will use a combination of molecular, cellular, biochemical, and genetic techniques to define the role of Erbin in NRG-mediated AChR transcription and to determine involved mechanisms. Specifically, we will 1) study the role of Erbin in NRG-mediated transcription of the AChR epsilon-subunit gene; 2) clarify whether Erbin inhibits Ras activation or binds to active Ras to prevent Raf activation; and 3) define structural elements necessary for Erbin inhibition ofNRG-mediated Erk activation. The resulting data will provide a better understanding of how NRG signaling and NRG-induced AChR expression are regulated at cellular levels. Such knowledge will contribute to our understanding of neurological disorders at the NMJ.